Metallocene compounds are useful as catalysts and various metallocene compounds have been known.
Several synthesizing processes are known as processes for preparing a useful metallocene compound. However, in substituting the halogens of metallocene dihalide with a substituent, if the substituent has a high molecular weight, makes the substituted product bulky, or is an aromatic compound, etc., there have been problems that an exchange reaction of the halogen does not proceed sufficiently, resulting in a reduced yield and that a large amount of by-products are produced which makes post-treatment difficult.
For example, a conventionally known process for synthesizing an aryl metallocene compound is to react a metallocene dihalide with an aryl alkali metal compound at room temperature or at the reflux temperature of a solvent employed for the reaction (as described in L. Summers et al., J. Am. Chem. Soc., 77, p.3604, (1955), M. D. Rausch et al., J. Organometall. Chem., 10, p.127 (1967), etc.). However, since the above-described process is accompanied with the side reaction such as reduction of the metal atom of a metallocene, a target product cannot be obtained in a high yield. In order to obtain a high-purity aryl metallocene compound, an additional step for purification such as recrystallization is necessary, which is not economical.
On the other hand, known is a process for synthesizing a diaryl metallocene compound by reacting a metallocene dihalide (e.g., metallocene dichloride) with an aryl alkali metal (e.g., an aryl lithium) in a polar solvent at 0.degree. C. or lower (as described in JP-B-2-34360, JP-B-63-60027 and JP-B-63-60028: the term "JP-B" as used herein means an "examined published Japanese patent publication"). This process requires the use of an expensive and highly dangerous chemical such as an alkali metal or diethyl ether. The alkali metal is very dangerous in handling because it ignites by the water content in the air. In addition, the alkali metal must be used in an amount not less than 2 times the theoretical amount, which necessarily leads to a cost increase. Since the target aryl metallocene compound is an industrially useful catalyst for preparation or hydrogenation of a high-molecular weight compound having a high stereoregularity, there is a strong demand for the development of its preparation process which is safe and inexpensive, which facilitates post-treatment and which permits preparation in a high yield.
In addition, known is a process for preparing a mono-substituted metallocene compound by reacting a metallocene dihalide with an alkyl Grignard reagent (as described, for example, in W. P. Long et al., J. Am. Chem. Soc., 82, p.1953 (1960), H. C. Beachell et al., Inorg. Chem., 4, p.1133 (1965), etc.). A preparation process of a di-substituted metallocene compound is however not described in the above documents.
A process for synthesizing a di-substituted dimethyl metallocene compound by reacting a metallocene dihalide with a methyl Grignard reagent at 25.degree. C. in a solvent of THF is also known (as described in T. S. Piper et al., J. Inorg. Nucl. Chem., 3, p.104 (1956), etc.). The yield brought by this process is, however, 1% and is markedly low. It is reported in WO97/09336 that a di-substituted dimethyl metallocene compound can be obtained in a good yield by reacting a metallocene dihalide with a methyl Grignard reagent at -5.degree. C. for 10 minutes or -5.degree. C. for 1 hour.
A process for preparing a di-substituted metallocene compound having a substituent other than a methyl group by using a Grignard reagent has not yet known and a process for preparing such a di-substituted metallocene compound at a high purity in a high yield sufficient for industrial production is desired.
An object of the present invention is therefore to solve the above-described problems upon synthesis of a metallocene compound and to provide a process for safely and easily synthesizing, at a low cost and in a high yield, a di-substituted metallocene compound substituted with an aryl, benzyl or diaryl phosphinomethylene group.